Twenty-eight chinchillas received continuous or intermittent infrasound (1, 10. 20 Hz) at 150, 160, or 170 dB SPL; there were 7 controls. Serial sections of the temporal bones were examined using light microscopy. Pathologies noted were tympanic membrane perforation, stapes subluxation, bleeding from the middle ear mucosa and tensor tympani, strial pathology, Reissner's membrane rupture, endolymphatic hydrops, saccular wall rupture, hair cell damage, and blood in the cochlear scalae. Continuous infrasound was more damaging than intermittent. Only continuous infrasound produced saccular pathology and perforations of the tympanic membrane. Of the other pathologies observed, continuous infrasound exposures produced 67% of the hair cell damage, 73% of the bleeding in the cochlear scalae. 83% of the strial pathology, and 78% of the cases of cochlear hydrops. 170-dB infrasound exposures produced the highest percentage of ears with pathologies of the three exposure intensities. As frequency increased the percentage of ears with pathologies decreased.
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